Ubuntu is completely unaffiliated with Flatpak and does not ship with flatpak preinstalled

You are thinking of snap

You can't even get away with a quadruple homicide these days

What has the world come to

Nintendo is going to make money no matter what

That stuff is expensive

It is just a license though

Both of those are dying unfortunately

I like blurays but at some point we need go acknowledge the truth

Handbrake takes a lot of resources already since it does video transcoding. I don't know what you mean by "convenient for Ubuntu."

You need to give more details if you want people to help you.

What's wrong with flatpak? Outside of a few limitations, flatpak generally makes things easier

OpenWRT has a zone based Firewall just like OPNsense does. Sure it isn't as clean but I don't really see a usecase for OPNsense that OpenWRT couldn't fulfill

Do you need VXlan? Unless you are doing something really funky, regular vlans should work fine. VXlan is only really useful in very large environments where you want to have layer 2 traffic flow over layer 3 networks. I would strongly recommend that you just stick to regular vlans since they are simple to work with and all you need is a router somewhere on your network to terminate the connection.

I personally would not recommend this setup as any issue with your proxmox cluster will turn into a network issue.

Instead, I would purchase a cheapish router that can run OpenWRT. If you are dead set on OPNsense you can find x86 boards from various vendors or you can make a dedicated router out of a network card and a small form factor computer